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Ultrasonic-NDT
| Question | Answer |
|---|---|
| What is a probe or transducer? | An ultrasonic device that houses a crystal that is capable of producing an ultrasonic pulse. |
| What is a couplant? | A material that is placed between two solids to assist in the passage of ultrasonic energy. |
| What is the purpose of a couplant? | To removes any (air) interference with the ultrasonic energy. |
| What material is a couplant made out of? | Liquids and pliable solids |
| What is impedance? | The amount (ratio) of the sound (pressure) to volume displacement at a given surface in a sound transmitting material. |
| What is interface? | A transition region between two materials of different impedances which are in acoustical contact. |
| What is a cathode ray tube (CRT)? | |
| A complex electronic device that when fed with an external signal, is capable of analyzing the signal and presenting it in the firm of an electronic picture. The picture is time based. | |
| What is time based? | The green line on the bottom of the face of the cathode ray tube. It's produced by an electron beam which sweeps across the screen at a constant speed. |
| What is a time sweep or Range? | The period of time required for the ejection spot to travel from one end of the screen to the other. |
| What controls the time sweep? | The range button |
| What is calibration? | Calibration is the act of adjusting a machine so that measures properly. |
| What does the term "phase" mean? | A phase is a part of a wave. 1 phase is above the Baseline, one below. |
| What does "rectified" mean? | Changed |
| What are the three basic processes involved in ultrasonic testing? | * sound is sent into the specimen * specimen modifies the sound and sends it back * the system displays the response as an electrical signal |
| Which part of the ultrasonic system displays the signal received from the specimen? | The CRT screen (cathode ray tube) |
| Let's say a wave travels at 2m/sec. It takes 4 sec for the wave to go through a specimen and return to its studying point. How thick is the specimen? | 2*4=8___8/2=4___ 4 meters |
| What is an interface? | A transition (border or boundary) region between two materials of different impedance (thickness) which are in acoustical contact. |
| In terms of reflection, what is the difference between a plastic/air interface and a plastic/steel interface? | An air gap (plastic/air) will not support ultrasonic energy, little or no energy will go into the specimen, it will reflect back into the probe |
| Why do wet have to calibrate on the same type of material we are going to test? | So the velocity is the same in the transducers and test part. |
| Let's say we are going to measure the thickness of a piece of mild steel we calibrate on a piece of cast iron. What will or readings for the steel specimen be? | To low (I.e. To thin) |
| Why is a couplant necessary in ultrasonic testing? | To get all air gaps or bubbles out of the space between the probe and the part. |
| What are the two important factors in the production of sound? | *A medium *external stimulants |
| What kids of materials create a medium in ultrasonic testing? | *Air *Water *Glass *steel |
| What is the purpose of a medium? | The external stimulus sets the particle of the medium into vibratory motion. |
| The movement of sound through material consist of what two parts? | *Compression (generates heat) positive charge *Rarefaction (absorb heat) negative charge |
| How do you define Amplitude? | *The amount of a molecules movement from its average (baseline) position *The amount of compression or rarefaction *The distance from the rest position to top. |
| Define "Frequency".... | *The number of cycles for a given time. *The time used is the second or microsecond |
| What is the difference between what we call "normal" sound and ultrasound? | The frequency |
| The human ear can hear sounds up to approximately....... | 20,000 cycles/second (20 kHz) |
| What are sounds above 20kHz are classified as? | Ultrasonic |
| What is dissipation/attenuation? | The spreading out and loss of energy |
| What does dampen mean? | To diminish progressively in vibration (ringing) |
| What is the definition of "wavelength"? | *The distance from one crest (top) to the next *the distance required for one complete cycle. *length from the beginning of compression to the ending of the successive layer of rarefaction |
| What is the formation of successive layers of compression and rarefaction across a dimension of a material for an indefinite period of time? | Continuous sound |
| What is the successive layers of a material for a definite period of time? | Pulsed sound |
| What is density? | Mass per unit volume |
| What is elasticity? | The "springiness" of the material |
| What is more important, the density or elasticity? | Elasticity |
| What do you use to determine what frequency of transducers to use for a particular test situation? | |
| Velocity formula (V=FW) | |
| What determines the wavelength? | The frequency |
| What determines the size of the defect that can be found? | The wavelength |
| The frequency chosen should be one that produces a wavelength ____________ __________ the critical defect size. | Two times |
| What is the Dcrit? | Diameter of the critical defect |
| How is "V" or velocity measured? | Inches/second, MM/SEC, CM/SEC |
| How is frequency measured? | Hertz (Hz), kilohertz (kHz), or megahertz (MHz) |
| How is a wavelength measured? | Inches, centimeters, or millimeters |
| What are "L"or longitudinal/compression waves? | Waves in which the particles vibrate back and forth in the same direction. |
| What will longitudinal/compression waves travel through? | They will travel through solids, liquids, and gases |
| What are shear waves? | |
| What are shear/transverse waves? | Waves in which the particles move perpendicularly to the direction of transmission. Shear waves will be about 1/2 the velocity of an "L" wave. |
| What do shear/transverse waves move through? | Solids or near solids only |
| What will shear/transverse waves NEVER move through? | *Liquids *gases |
| What are surface/Rayleigh waves? | |
| Transverse waves which travel along the surface in an elliptical orbit, they do not go deep into the material. | |
| In surface/rayleigh waves the major axis of the ellipse is (1)____° to the surface and the minor axis is (2)____° to the direction of wave movement. Velocity is (3)____-____% that of shear wave. | (1) 90° (2) 90° (3) 90-95% |
| What are the two types of Lamb/Plate waves? | *symmetrical waves *asymmetrical waves |
| In symmetrical waves there is an even _________ from the center of the wave. | Displacement |
| Asymmetrical waves are........ | Shear waves |
| In Lamb/Plate waves the (1)________ is dependant on the material tested, the (2)________ of the wave and the (3)_________of the material. | (1) velocity (2) frequency (3) thickness |
| Straight beam testing involves what waves? | Compressional waves |
| An angle beam testing _______are sent into the specimen... | Shear waves |
| In immersion angle beam testing, the probe is set at an ______ to the surface of the specimen... | Angle |
| What is placed between the transducer and the specimen and contact angle beam testing? | A wedge |
| What is a limitation to contact testing? | You do not know exactly where the defect is. |
| In contact testing, what sound is used? | Continuous sound |
| How many transducers are used on contacts testing? | Two |
| In pulse-Echo contact method what kind of beams are used? | *angle beam *straight beam |
| In puls-Echo contact, the transmitting transducers are made of what crystals? | Barium titanate |
| In pulse-Echo contact, the receiving transducer crystal is made of what? | Lithium sulfate |
| In pulse-Echo contact, the probes are also called ___________? | Pitch/Catch |
| What can an angle beam testing be useful on? | *Welds *testing pipes |
| What is used for couplant in immersion testing? | Water |
| In immersion testing, the sound and the part may be either _______ or _______ depending on the angulation of the probe. | *Compressional * Transverse |
| What is one variation of immersion testing called? | The Delta technique |
| What are the four wave nodes? | *longitudinal wave/compression wave * transverse wave/Shear wave * surface wave/rayleigh wave * lamb wave/plate wave |
| Which travels faster, a Shear wave or a longitudinal wave? | A longitudinal wave |
| What are the two basic ultrasonic methods? | *contact testing * immersion testing |
| What kinds of waves are produced by a straight beam probe? | Compressional waves |
| What kind of waves are produced by the crystal in an angle beam probe? | Longitudinal or compression |
| Do we get back wall Echoes In all kinds of ultrasonic testing? | No |
| What kind of ultrasonic testing has no back walls? | *angle beam testing * Delta technique |
| True or false, a cycle can be defined as the beginning of the compression to the end of the successive layer of a rarefaction. | True |
| True or false, probes are also called transducers | True |
| True or false, when an ultrasonic signal reaches an acoustic interface, all the ultra Sonic energy is transferred, or passes through the interface, to the new | False |
| True or false, if you are Velocity is 1 inch per second and the signal takes 2 seconds to return, your part is 1 inch thick. | True |
| True or false, the wavelength determines the size of the defect that can be found. | True |
| What is ultrasound? | A sound which has a frequency pitch above the range of the human ear |
| What is the process of comparing an instrument or device with a standard called? | Calibration |
| Why is cuplant required in ultrasonic testing? | To exclude the presence of air between the transducer and the test material |
| What is a material used between the face of a search unit and the test Surface to permit or improve the transmission of the sound beam from the search unit to the test specimen called? | A couplant |
| How is a wavelength calculated? | Dividing velocity by frequency |
| An ________ is a transition region between two materials of different impedances... | Interface |
| A ultrasonic device that houses a crystal is called a ________ and is used to generate and receive ultrasonic pulses... | Probe |
| What is another name for a probe? | *Transducer *Search unit |
| What are two important factors in the production of sound? | A medium and an external stimulus |
| What is the term used to indicate cycles per second? | Frequency |
| A cycle consists of what two parts? | Compression and rarefaction |
| Compression ___________ heat. | Generates |
| Rarefaction _________ heat... | Absorbs |
| ______________ is the amount of compression or rarefaction, or it can also be the distance from rest to the peak of the signal. | |
| Amplitude | |
| What is piezoelectricity? | Pressure electricity |
| What is sensitivity? | The ability to detect echoes from small discontinuities |
| What is resolution? | The ability to separate the echoes from two targets close together |
| Which type of piezoelectric material is the best receiver? | Lithium sulfate |
| What is the relationship between the thickness of a crystal and the frequency of the sound it sends out? | The thinner the crystal, the higher the frequency |
| What is the function of the plastic wedge in an angle beam transducer? | It will convert longitudinal waves to Shear waves. |
| What does the designation, "RM" mean when used for a connector? | Right angle microdot |
| What is a paintbrush transducer used for? | Rapid scanning |
| What is the purpose of sound-tunnel and Leading-Edge serrations in perspex wedges? | It dampens The Sound being reflected within the wedge. |
| What are the main types of piezoelectric material used in non-destructive testing? | *quartz *Lithium sulphate *polarized ceramic materials |
| What is the polarized ceramic materials made from? | *Barium titanate *Lead Methaniobate |
| _________ _________ are grown in a solution of _________ _______ and water. | *Lithium sulphate *Lithium sulphate |
| What are the best crystals to use an immersion testing? | Lithium sulfate crystals |
| What is the best overall Crystal to use? | Lead Methaniobate |
| What is a disadvantage for lead Methaniobate crystals? | The only disadvantage is its characteristic frequency to its thickness. |
| What Crystal makes the best receiver? | Lithium sulfate |
| What crystal is the best transmitter? | Barium titanate |
| What is designed to dampen reflected sound within a test piece? | A wedge |
| What are the three basic groups in the CRT machine controls? | *Display controls *timer controls *Pulser/receiver controls |
| On the CRT machine, the vertical control moves what? | Time base line up and down |
| On the CRT machine, what does the horizontal control move? | It moves the time Baseline left or right. |
| On the CRT machine, what does the intensity control? | Controls the brightness of the CRT display. |
| On the CRT machine, what sets the sharpness of the trace line? | Focus control |
| On the CRT machine what does the astigmatism control? | It corrects for Distortion caused by changing Transit time of the Electron Beam across the CRT face. |
| On the CRT machine what controls the cycle of transmitting and receiving pulse? | Rate or repetition rate control |
| What causes the phosphor compound on a CRT screen to Glow? | High-speed electrons |
| Which type screen presentation is most common in ultrasonic testing? | A-scan |
| With a logarithmic display, what happens to the height of a signal when we add 6 decibels? | It will increase the signal height a definite number of millimeters. |
| What is an unrectified wave? | It shows both positive and negative waves. |
| What is half-rectified? | It shows the positive side of the wave. |
| What are fully rectified waves | It shows both negative and positive waves on the positive scale. |
| On the CRT display controls, what does the vertical control move? | The time base line up and down. |
| On the CRT display controls, what does the horizontal control move? | The time base line left or right. |
| On the CRT display controls, what does the focus control move? | It sets the sharpness of the trace line. |
| On the CRT display controls, what does the astigmatism control? | This corrects for distortion caused by changing transit time of the electron beam across the CRT face. |
| On the CRT display controls, what does the power and scale illumination control? | This turns the power on and controls the edge lighting. |
| On the CRT display controls, what does the rate or repetition rate control? | The controls the cycle of transmitting and receiving pulses. |
| On the CRT timer controls, what does the sweep delay control and how do the indications appear? | The sweep delay control moves all the indications along the time base line. The horizontal control moves the ENTIRE base line. |
| On the CRT timer controls, what does the sweep length or range control alter? | This control changes the spacing between indications. |
| On the CRT timer controls, how does the sweep length or range control move? | This expands or contacts the base line, ALWAYS away from or toward the left side of the screen. |
| On the CRT pulser and receiver controls, what does the pulses length control move? | Adjusts time duration of the high frequency pulser applied to the transducer. |
| On the CRT pulser and receiver controls, what does the pulses tuning move? | Compensates for the slight electrical differences between the transducer and electric cable. (Adjusting impedance control) |
| On the CRT pulser and receiver controls, what does the reject control move? | Suppresses signals which are below a certain amplitude and is used to eliminate unwanted signals from the CRT. (Similar to the "gates") |
| On the CRT pulser and receiver controls, what does the sensitivity or dB (decibel) control move? | It controls amplification of the signals sent to the receiver/amplifier. |
| On the CRT pulser and receiver controls, what does the frequency control move? | It times the receiver-amplifier circuit to the frequency of the transducer. |
| On the CRT pulser and receiver controls, what does the mode selector control? | It allows testing technique selection (pulser-echo, through transmission, pitch/catch) |
| On the CRT pulser and receiver controls, what are the two kinds of connectors? | *"T"-transmit receptacles *"R" -receive receptacles ("T" is used in pulse-echo) |
| What is an A-scan presentation? | Gives a time vs amplitude display |
| What is the most used scan presentation? | A-scan (linear scan) |
| What can an A-scan not provide? | A permanent indication or the type of discontinuity. |
| What is a B-scan presentation? | They are mostly used in the medical field and has a cross sectional view. No permanent indication is provided. |
| What is a C-scan presentation? | An automated system used in immersion testing which gives a picture similar to a radiograph showing a section of the specimen with contours of the discontinuities. |
| The _________ is a logarithmic means of expressing the ratio between one echo height and another; important when measuring amplitude and sensitivity. | Decibel |
| What are the two types of displays on the CRT? | *linear display *logarithmic display |
| Echoes from flat-bottom (FBH) will go down _______db (decibel) with double distances. | -12 |
| Echoes from drilled-through holes (DTH) will go down _________ db (decibel) with double distances. | -9 |
| Back wall echoes (signals) on a CRT screen will go down (decrease in amplitude) ________ db if the distance from the transducer to the back wall (thickness of the material) is doubled. | -6 |
| True or false..... Adding +6 db gain on the UT instrument will cause the signal on the CRT screen to double in amplitude? | True |
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